Contact Form 7 email sending issue

I am working on a project which has 5 different sites. On all of them I am using CF7. The problem is that on three of them it works fine and emails are being sent successfully. But on the other two websites no emails are being sent despite using the same credentials and every other plugin is also same. In fact the other two websites were created by copying one of the first three sites on which CF7 mail is working fine. But for some reason these two sites are showing an error “There was an error trying to send your message. Please try again later.” It is in the red border.

I have also tried using various SMTP plugins and still the issue is same. Also all five websites are hosted on same server and therefore similar email configuration exists for all of them.

So can anyone please help me in finding the probable causes and their solutions. I have already tried various solutions I could find on Google search but issue is still there. Thanks a lot.